Modern electrical devices such as communications transmitters often incorporate a balun for converting a differential signal into a single-ended signal. For example, a wireless transmitter circuit may employ a balun for converting a differential signal generated by the transmitter circuitry into a single-ended signal for further amplification and transmission over a wireless channel. A common balun implementation includes two mutually coupled inductive elements, configured such that a differential voltage across the first (primary) balun element generates a corresponding single-ended voltage across the second (secondary) balun element.
In the design of baluns for communications devices, the quality factor (or “Q”) of a balun is a key figure of merit. A higher Q generally leads to higher balun output voltage, along with better power transfer and signal-to-noise ratio (SNR) characteristics for the overall device. When the secondary balun element is coupled to subsequent loading stages, the Q of the loaded balun (or “loaded-Q”) may be reduced due to the presence of resistive load elements, causing poorer overall device performance.
It would be desirable to provide simple and efficient techniques for improving balun loaded-Q.